The present invention relates to program controllers or programmers, as they are sometimes called, which are employed for sequentially actuating a plurality of switches for controlling various functions of an appliance or other device to be controlled. Controllers of this type are commonly employed for household appliances, such as dishwashers, clothes washing machines, clothes dryers, and cooking appliances. Typically, a subfractional horsepower timing motor drives an advance mechanism for effecting rotation of a cam drum; and, individual tracks on the cam drum sequentially actuate and deactuate program function control switches as the cam drum is rotated through a complete revolution which comprises the desired program cycle.
In applications where a rotatable cam drum is employed for programming the actuation and deactuation of the appliance control switches, the degree of sophistication of sequencing the switches is limited by the configuration of the cam and the rate of advance of the cam. Therefore, it has been desired to find alternative ways of controlling the program function switches in an appliance to avoid the limitations of a sequentially advanced cam track.
In attempting to overcome such limitations, appliance programmers having solid state electronic switching devices have been employed. However, such switching devices have required the use of relays where switching of heavy current is required for controlling motor starting and other functions requiring a substantial current draw. In addition, the cost of providing such components to the appliance programmer or controller has rendered the electronic controller noncompetitive against equivalent electromechanical programmers in high volume mass produced household appliances is.
Thus, a need has arisen for finding a way or means of controlling the program sequence of appliance functions in a manner which can provide for the switching of substantial current as, for example, the starting current for a main drive motor, and yet provide for a programmed sequence control which is not limited by the positioning of sequentially advanced cams on a rotating cam drum. It has thus been desired to employ the sophistication and the variety of control sequence programming available from a programmed microcomputer or microprocessor, which can provide for control of the appliance functions independently of a timed rate of rotation of a cam.
Accordingly, it has been desired to find a technique or a way of providing a plurality of individual switches for controlling selected appliance functions which draw substantial current and to control the sequence or program of operation of such functions with a microcomputer. It has further been desired to provide such programmed controlling in a manner which is low enough in cost to enable the resultant programmer to be used in mass produced household appliances which are sold in a highly competitive marketplace.